A Gerber bridge having a hinge section or a connecting section in a continuous girder not only has the same advantages as those of a continuous bridge, but also is externally, statically determinate, so that differential settlement of supporting points does not occur in a Gerber bridge, and a Gerber bridge is not influenced by temperature changes. In addition, since it is possible in a Gerber bridge to decrease dead-load stress in comparison with a single girder, a Gerber bridge is advantageously adopted in a long span, a cross-section of which is dominated with dead-load. Thus, a Gerber bridge is often used as a steel made bridge or a concrete made bridge reinforced with steel bars.
There have often occurred breakages of bridges caused by rapidly increased traffic volume and heavy loads mounted on a heavy trucks. In particular, bridges established in accordance with old standard not only become obsolete, but also decrease its load-resistance due to repeated load from heavy trucks and corrosion due to salt damage. Among such bridges, a hinge section of a Gerber bridge is heavily damaged, and a crack occurs, in particular, because of shearing forces in a lot of hinge sections of existing Gerber bridges.
The damage of a hinge section of a Gerber bridge is characterized by:
(a) vertical crack of a support due to concentration of horizontal stress caused by expansion and contraction of girders which is caused by insufficient movement of a support of a hinge section, or by earthquake; PA1 (b) deterioration and corrosion of reinforcing steel caused by water leakage from an expanded or contracted portion; and PA1 (c) oblique cracks in corners caused by lack of resistance to bending moment and shearing force.
As is seen in a bridge accident which recently occurred in Korea, if a hinge section is heavily damaged, the bridge itself may fall. Thus, it has long been an object to establish a reinforcing structure of a hinge section.
A conventional method of reinforcing a hinge section of a Gerber bridge is to fill the space in a hinge section with epoxy resin. However, in this method, girders are merely the adhered to each other by means of adhesive force of the epoxy resin. This method is somewhat advantageous if epoxy resin is filled before a hinge section is damaged, but cannot provide sufficient advantages once a hinge section has been damaged.
In another conventional method, a cable is formed between horizontal girders by means of which a reaction force is supported at the hinge section. Since almost all work for carrying out this method can be done on a lower surface of the bridge, it is possible to accomplish reinforcement construction without prohibiting vehicles from running on the bridge. However, a horizontal girder to which the cable is fixed unperferably receives a large horizontal load which has not been taken into consideration at initial design. In addition, this method cannot provide essential repair to a damaged hinge section. Furthermore, the cable is kept exposed to the atmosphere, and it is not preferable to use a cable in such a condition.
In still another conventional method, a cable is spanned between support girders which supports a girder hung from a hinge section, and a pre-stress is introduced to the hung girder by means of an out-cable system. However, a fixed girder supporting a hung girder therewith receives a large horizontal load. In addition, as the introduced pre-stress decreases, it becomes more difficult to stably keep the reinforcement effects.
In view of the foregoing problems in prior methods of reinforcing a hinge section, it is an object of the present invention to provide a reinforcement structure for a hinge section which accomplishes superior reinforcement effects and long-term stability.